Radiation-induced xerostomia (dry mouth syndrome) is a common side effect in head and neck cancer patients caused by off-target effects of radiation therapy that damage the salivary glands. This condition leads to hyposalivation, oral infections, tooth decay, difficulty speaking, and impaired digestion, among other complications, in ~40% of patients. While amifostine, an FDA-approved drug to prevent this condition, can be administered to patients, its clinical usefulness is limited, as severe vomiting in many patients requires discontinuing treatment. Discovery of alternative drugs is hindered by a lack of relevant in vitro models, as salivary gland cells rapidly lose the organization and secretory function when removed from the body. To address this technological challenge, we propose the use of a unique system combining microbubble (MB) array technology with poly(ethylene glycol) (PEG) hydrogels to create a favorable microenvironment for salivary gland tissue mimetic growth in vitro. MBs are separated spherical cavities with 200 m openings and ~40 nL volume formed in polydimethylsiloxane (PDMS). MBs are arranged in an array- based format for high-throughput screening and the unique spherical shape has been shown to concentrate paracrine/autocrine factors to allow cells to condition their own microenvironment. Matrix metalloproteinase (MMP)-degradable PEG macrogels (1 mm x 5 mm discs) have been shown to promote tissue mimetic structure and maintenance of biomarker expression through encouraging cell-cell and cell-matrix interactions. The central hypothesis is that the combination of these two techniques will improve the in vitro microenvironment of salivary gland tissue mimetics and provide an effective platform for high-throughput screening of preventative drugs for radiation-induced xerostomia. To address this hypothesis, three aims have been identified. In-chip assays will be developed to analyze the secretory function of salivary gland tissue mimetics in MBs (amylase, mucins, lysozyme; Aim 1A) and their response to radiation damage (caspase, ?H2AX, PrestoBlue?, EdU; Aim 1B) by adapting macroscale (e.g. 96-well plate) assays/characterization techniques. Aim 2 will identify proteins/peptides that provide instructive cues for promoting secretory function and organization similar to native salivary gland tissue, as measured by assays developed in Aim 1A. Preliminary testing of radioprotective drugs will occur in Aim 3, where a selected list of radioprotective drugs will be screened through the MB-hydrogel system and compared to amifostine, the currently approved therapy. This project is significant for public health, as it will provide important preclinical testing for new drugs to prevent radiation-induced xerostomia. It will impact the research community by providing a unique high- throughput drug screening platform that can be adapted for other tissues.